Chemotherapy-resistant leukemias and sarcomas contain tumor-specific chromosomal translocations that encode fusion-proteins and these fusion-proteins are expressed only in the tumor. A fusion-protein provides significant tumor target specificity and increases the likelihood that novel therapies targeting the fusion-protein will be both effective and lack non-specific toxicity. Many of the tumor-specific fusion-proteins that function as transcription factors are disordered proteins. Disordered proteins lack the rigid alpha-helical or beta sheet structures required for structure-based drug design. While disordered proteins require a more empiric approach to the discovery of small molecule protein-protein interaction inhibitors, the biochemical properties of disordered proteins may actually favor the success of protein-protein interaction inhibitors. We will develop a novel paradigm to inhibit the protein-protein interaction of an oncogenic fusion protein. The Ewing's Sarcoma Family of Tumors (ESFT) contains a characteristic translocation, t(11:22), which leads to the oncogenic, fusion-protein, transcription factor EWS-FLI1. Therapies that inactivate EWS-FLI1 might address the significant problem of recurrent disease for patients. Since EWS-FLI1 lacks intrinsic enzymatic activity, and is a disordered protein, we will create novel protein-protein interaction inhibitors to block EWS-FLI1 binding to critical protein partners. We identified RNA Helicase A (RHA, p150), a DEAD/H family member that modulates gene expression, as a critical partner of EWS-FLI1. EWS-FLI1 binds to a unique region of RHA that is NOT involved in non-malignant RHA transcriptional modulation. A peptide mimic of this binding region inhibits EWS- FLI1 binding to RHA and we have discovered a lead compound, NSC635437, which has significant structural homology with the peptide mimic. A derivative small molecule of NSC635437, YK-4-279, blocks RHA binding to EWS-FLI1 and induces apoptosis in ESFT cells. We hypothesize that the interaction of RHA with EWS- FLI1 results in a potent transcriptional activator/coactivator complex, which amplifies the functions of both proteins and drives the malignant phenotype of ESFT. Our approach will develop reagents that prevent the binding of EWS-FLI1 to RHA, both to address our hypothesis and create a new therapeutic agent. We will accomplish our objectives by examining the effects of blocking RHA from enhancing EWS-FLI1 function, first using a peptide and then with small molecule protein-protein interaction inhibitors. We will work together with Dr. Milton Brown, a highly regarded medicinal chemist, to chemically optimize our lead compound. Our work has broad applicability to a larger group of tumors, serving as a new paradigm for developmental therapeutics. This paradigm to create small molecule inhibitors of EWS-FLI1 could be used for other translocation-defined malignancies such as chemotherapy-resistant carcinomas, sarcomas and leukemias. Therefore, future work would have a strong potential for a positive impact upon many patients with difficult to treat tumors leading to reduced mortality and morbidity. PUBLIC HEALTH RELEVANCE:New targeted therapies are needed for cancer patients that improve survival and decrease side-effects of therapy. Ewing's Sarcoma Family of Tumors (ESFT) are highly malignant tumors of bone and soft tissue that occur in children, adolescents, and young adults. The tumors often grow in close proximity to bone, but can occur as a soft-tissue mass. Current standard therapy for ESFT patients is a five-drug regimen that lasts for approximately 9 months. Patients who present with localized ESFT have approximately 70% disease-free survival. Patients who present with metastatic ESFT have a poor prognosis (20% disease-free survival) despite intensive therapy. These clinical response rates have persisted for the past decade, even after dose-intensifying chemotherapy and bone marrow transplantation. Therefore, we need to discover novel therapeutic approaches to both reduce treatment related morbidity and improve overall survival. Fortunately, ESFT contain an ideal molecular target. Unfortunately, despite knowledge that inactivation of this ideal target causes ESFT cell death, strategies to inactivate the molecular target have not been brought to the clinic. This project will specifically address the need for new targeted therapies for ESFT and a large number of related malignancies that have chromosomal translocations.